Demon

Demons
In the world of Devil May Cry, there are two major lifeforms: Humans, and Demons. Demons are beings from a separate realm known as the Demon World or Hell. The nature of demons is yet to be clearly defined.

Demons come in many different shapes and sizes, ranging from shapeless blobs to being nearly indistinguishable from humans.

Powers
Demons are naturally more powerful than humans and are able to preform magical and supernatural feats.

The abilities of demons is greatly varied. They usually seems to possess powers that are based on a certain element (ie: fire, lightning, earth, etc.). After a demon is killed, it seems possible to absorb that demons soul and manifest their power and/or manifest that power into a weapon (These are known as "Devil Arms").

Though demons naturally more powerful then humans, and posses abilities beyond that of any human, that does not prevent humans from being able to fight and even kill a demon (though humans with this ability seem to be very rare and have spent much of their life training to do so).

The power of a demon is greater when they are in or connected to the demon world. If they are cut off from the Hell, their power is greatly reduced.

Interestingly, in Devil May Cry 4, Dante suggests that when a demon becomes selfless and/or loves, that is when they can achieve greater power.

Nature
Demons, generally, are very selfish and "evil," often seeking to increase their own power or influence. For demons, the stronger you are, the more power you have. Very rarely do demons ever show remorse or pity, particularly when regarding humans.

Demons and Humans
Demons view themselves as superior to humans and as such wish to rule the human world as well as their own. It is implied that before Sparda's uprising, the demons held dominion over the human world and there were many gates and portals between the two realms. Ever since Sparda sealed off the Hell from the human world, demons have been attempting to regain dominion over the humans.

Though demons are thought of as "evil", Dante has also described humans as having the same quality, and that in many cases they are even worse. There have been a few humans who seek to gain demonic power themselves.

Angels
A few times throughout the Devil May Cry series, beings are described as "angels." These beings do not seem to be a separate being from demons, but rather, just a different name for them. Worth noting is that every being described as an angel, was once human or part human. Perhaps the term "angel" describes a human (or part human) who has become a demon.